1. Field of Invention
This invention relates to a manufacturing method of forming a ball grid array package. More particularly, the present invention is related to a manufacturing method of forming a ball grid array package for enhancing the stiffness of the substrate strips and avoiding the substrate strips from being warped before the substrate strips are separated into a plurality of individual substrate units encapsulated in said ball grid array package.
2. Related Art
In this information explosion age, integrated circuits products are used almost everywhere in our daily life. As fabricating technique continue to improve, electronic products having powerful functions, personalized performance and a higher degree of complexity are produced. Nowadays, most electronic products are relatively light and have a compact body. Hence, in semiconductor production, various types of high-density semiconductor packages have been developed. However, ball grid array packages are the main assembly products and packages recently.
As mentioned above, a conventional ball grid array package mainly comprises a chip and a substrate. The substrate has an upper surface and a lower surface. The chip is disposed on the upper surface; the substrate has a plurality of conductive traces formed therein for electrically connecting the upper surface and the lower surface; and the chip is electrically connected to the conductive traces of the substrate by a plurality of wires. In addition, an encapsulation material is provided to form an encapsulation body to enclose the chip, the wires, and to cover the upper surface of the substrate. Furthermore, a plurality of solder balls are formed on the lower surface of the substrate to be regarded as external terminals or contacts for electrically and physically connecting to external devices.
Refer to FIGS. 1 and 2, which disclose the progresses of manufacturing a conventional ball grid array package 60. Therein, a substrate strip 30 having a plurality of substrate units 20 is provided as shown in FIG. 1. Therein, each of the substrate unit 20 has an upper surface 22 and a lower surface 24 respectively. A plurality of chips 10 are disposed on the upper surfaces 22 of the substrate units 20. Therein, said each upper surface has at least one chip formed thereon. Next, a plurality of encapsulation bodies 40 are formed on each of the upper surfaces 22 of the substrate units respectively and cover the chips 20 respectively. Furthermore, a plurality of solder balls 50 or other electrically conductive devices are formed on the lower surfaces 24 of the substrate units 20. Finally, a singulation or dicing process is performed to separate the encapsulation bodies 40 from each other so as to form a plurality of ball grid array packages 60 with said encapsulation bodies enclosing the chips therein.
However, as shown in FIG. 3, the coefficient of thermal expansion of the substrate strip 30 is much different from that of the encapsulation bodies 40. Hence, when the encapsulation bodies 40 are cooled down to the room temperature, the substrate strip 30 with the encapsulation bodies 40 formed thereon will be warped. De facto, the substrate strip 30 is usually warped at the interconnection between the substrate strip 30 and the encapsulation bodies 40. When the substrate strip 30 is warped, the solder balls 50 or other conductive terminals formed on the lower surfaces 24 of the substrate units 20 are not coplanar with each other. Hence, when the substrate strip 30 with encapsulation bodies 40 formed thereon is singulated or diced into a plurality of individual substrate units 20 through the cutting line 12 and then the individual substrate units are disposed on a printed circuit board, it is very difficult to well dispose the individual substrate units 20 on the printed circuit board. In addition, the warpage will become larger and larger accompanying with the increase of the width or length of the substrate units and the reduction of the thickness of the substrate units 20. In other words, the warpage will restrict the design freedom of the thickness of the substrate units and the size, such as length or width, of the substrate units.
Therefore, providing another manufacturing method to solve the mentioned-above disadvantages is the most important task in this invention.